1. Field of the Invention
The invention relates generally to systems and methods of optical micro-assemblies. In particular, the invention relates to passive alignment micro-assembled optoelectronic modules forming multichannel parallel optical systems with optical transmitters, including monitor photodetectors, and optical receivers.
2. Description of the Related Art
Optoelectronic systems used for communications usually consist of an optical transmitter and an optical receiver. The optical transmitter usually consists of a plurality of light emitting devices to generate light signal and encoder structures to encode electrical signals into optical signals by modulating the light, a plurality of light coupling elements (such as lenses, mirrors, gratings) and a plurality of fibers used to carry light signals along a distance. The receiver usually consists of a plurality of photodetectors to decode optical signals into electrical signals, a plurality of light coupling elements, and a plurality of fibers. For relatively short-distance data communication applications, the light emitting devices are usually surface-emitting lasers and the photodetectors are usually surface-receiving photodetectors.
The traditional TO (transistor outline) assembling technology places a single laser or a single photodetector on a TO base and affixes a cap having a lens window and a single optical fiber onto the TO base using passive or active alignment to form the whole TO package. A transmitter TO package may also include a mirror structure to deflect some laser light and a monitor photodetector to detect the deflected light for real-time laser power monitoring during practical operations. This well-established assembling and packaging method is limited in that the TO package is only able to contain a single photodetector, or a single laser and a monitor photodetector.
Ever increasing bandwidth demand for data transmission requires multiple-channel transmitters, receivers, or combined transceivers within a single package for higher density of total bandwidth per volume. Beginning with small form-factor pluggable (SFP) for single channel transceiver applications, a number of standard transceiver packages have been established by the industry, e.g. quad SFP plus (QSFP+) for four-channel transceivers, compact form-factor pluggable (CFP) for ten-channel transceivers. These multiple-channel transceivers, however, cannot simply adopt multiple traditional TO sub-packages due to the small form-factor of the package. Assembling a plurality of lasers (and monitor photodetectors), photodetectors, and fibers into a single and small platform, and placing the platform inside the standard multi-channel transceiver packages along with other electronic chips are the key technology for transceiver module manufactures.
Although active alignment packaging approach has been widely adopted in edge-emitting optoelectronics assemblies, passive alignment assembling processes, in which the fibers are aligned and attached to lasers or photodetectors without active adjustment, have the advantages of higher throughputs and lower costs than active alignment procedures. The existing prior passive alignment processes include: using a molded plastic fixture with a plurality of lenses and a reflector to hold a fiber and reflect the light; using an etched v-groove (or u-groove) trench to hold a fiber and an etched reflector to reflect the light; and using a through-substrate hole to hold a fiber and a flip-chip bonded laser or photodetector array facing the fiber facet on the substrate.